Preparation Of TiO₂/Carbon Composite Materials And Their Applications In Lithium/Sodium-ion Batteries

At present,much attention has been paid to energy storage technology.Energy storage technology has been used to wearable devices,mobile phones,laptops,electric vehicles(EVs)large-scale energy storage.Lithium-ion batteries(LIBs)have been widely applied to EVs and consumer electronics such as mobile phones and laptops,because of their excellent energy density,long lifetime.However,it is a great pressure to meet the demand for large-scale energy storage from limited lithium resources.As an alternative,sodium exhibits many similar physicochemical properties with lithium and other particular advantages.Consequently,sodium-ion batteries(SIBs)have logically been expected as the best candidate for the next generation rechargeable batteries in large-scale energy storage.Electrode materials,a vital part of lithium/sodium-ion batteries,have the function of ions storage.Here,we have investigated TiO2/carbon composite materials and their applications in lithium/sodium-ion batteries.The main research contents are as follows:(1)A coaxial frame architecture(GF-CF)of TiO2 connected to graphene foams was fabricated via chemical vapor deposition and hydrothermal process.TiO2 nanosheets are coaxially aligned on graphene foam framework as freestanding electrodes.The coaxial frame structure ensures the fast electron transportation and large interface between graphene and TiO2 to store more lithium/sodium-ion.And the in situ growth inhibits the aggregation of TiO2 nanosheets.Therefore,SIBs with GF-CF showed a discharge capacity of 136.0 mA h g-1(capacity retention is 88.0%)after 100 cycles with coulombic efficiency of 96.5%.According to cyclic voltammetry analysis,we find that capacitive effects contributed 45.1%in the total charge storage.When used for LIBs,GF-CF showed a discharge capacity of 150.0 mA h g-1 after 40 cycles with coulombic efficiency of 99.0%.(2)Carbon paper@TiO2 composite materials(CP@TiO2)has been synthesize via hydrothermal process.As freestanding anode electrodes,carbon paper in CP@TiO2 ensures the fast electron transportation.TiO2 nanosheets in situ grew on carbon paper,which can inhibit the aggregation of nanosheets.And more active sites will appear.Thus CP@TiO2 can store more sodium-ion than TiO2.Ohmic resistance and charge transfer resistance of CP@TiO2 are lower than TiO2.Meantime,the freestanding electrode can be directly assembled without current collector,conductive agent and binder,so reducing the cost and overcoming the adverse side reactions caused by these inactive components.